1. Field of the Invention
The invention relates to the sphere of rolled or extruded products such as sheets, profiles, wires or tubes made of AlMgMn-type aluminum alloy containing more than 3% by weight of Mg, intended for welded constructions having a high yield stress, good resistance to fatigue and good toughness for structural applications such as ships, industrial vehicles or welded bicycle frames.
2. Description of Related Art
The optimum dimensioning of welded structures made of aluminum alloy leads to the use of 5000 series AlMg alloys according to the Aluminum Association nomenclature, in the cold-worked temper (temper H1 according to the standard NF-EN-515) or partially softened temper (temper H2), or stabilized temper (temper H3), while maintaining high resistance to corrosion (temper H116) rather than the annealed temper (temper 0). However, the improvement in the mechanical characteristics relative to the temper 0 does not usually remain after welding, and certifying and monitoring organizations generally recommend that only the characteristics in temper 0 be taken into consideration for welded structures. The resistance to fatigue and the fissure propagation rate should also be taken into consideration for dimensioning.
In this sphere, research has concentrated mainly on the implementation of the welding operation itself. There have also been attempts to improve the corrosion resistance of the article by appropriate thermomechanical treatments.
Japanese patent application JP 06-212373 proposes the use of an alloy containing 1.0 to 2.0% of Mn, 3.0 to 6.0% of Mg and less than 0.15% of iron to minimize the reduction in the mechanical strength due to welding. However, the use of an alloy having such a high manganese content leads to a reduction in the resistance to fatigue and in the toughness.